In general, when a metal piece is immersed in water for a long time, the surface of the metal piece becomes corroded. Metal corrosion is caused by localized polarization of parts of the surface into an anode and a cathode. A small amount of electric current flows between the anode and the cathode, which causes an oxidation reaction at the anode and a reduction reaction at the cathode. The oxidation reaction at the anode oxidizes the surface of the metal piece, whereby the metal corrosion progresses.
Various kinds of devices capable of improving the quality of water with ceramics that emits far-infrared rays have been conventionally known as water quality-improving devices. An example of the water quality-improving devices may be a device named “THE BIOWATER” (registered trademark), which is sold on market by TOSHIKOGYO CO., LTD. (see Non-patent document 1). It is reported that water treated with this device has various advantages. Especially noticeable is its effectiveness in preventing deterioration caused by red rust. More particularly, metal corrosion progresses more slowly in water having been treated with this water quality-improving device than in untreated water. In other words, the treatment of water with the water quality-improving device enhances antirust effect of water. When the water quality-improving device is installed, for example, in piping, through which the water that has been treated with the water quality-improving device is made to pass, the progress of metal corrosion on the inner surface of the piping is capable of being controlled.
It normally takes a time period from a few months to several years to assess the progress of metal corrosion by observing and analyzing the surface of metal pieces immersed in water. Conventionally, it also takes a time period from a few months to several years from the installation of a water quality-improving device in piping to determine the effectiveness of the device in controlling metal corrosion on the inner surface of the piping. Thus, currently it is not possible to determine an improvement in the rust-prevention of treated water within a short time period from the installation.
Also, in general, a water quality-improving device is usually placed in piping of large facilities such as factories and buildings. When an improvement in the quality of water that has been treated with a water quality-improving device is determined by examining the piping in which the water quality-improving device is installed, it is necessary to temporarily stop operation of the equipment provided with the device, to drain water from the piping, and then to observe the inner surface of the piping. However, it is often practically difficult to stop operation of the equipment and it requires heavy labor to drain water from the piping. Thus it is difficult to check whether the anti-corrosion performance of water is enhanced owing to the installation of a water quality-improving device by examining the piping in which the water quality-improving device is installed.
A determination device for determining an improvement in water quality capable of determining an enhancement in the quality of treated water within a short time period has been proposed (patent document 1). This determination device for determining an improvement in water quality has excellent performance; “it does not take a long time period from a few months to several years to observe the progress of corrosion in order to determine the effectiveness of the device in controlling metal corrosion, but just a short period of several days to check an enhancement in the antirust effect of water.”
We will explain the technical significance of water quality improvement hereinafter, referring to the determination device for determining an improvement in water quality disclosed in patent document 1.
The inner walls of iron pipes for the distribution of city water, which contact city water, become rusty as a long time passes. Due to various factors, the inner walls of iron pipes have parts that easily rust, or anode parts, and parts that hardly rust, or cathode parts. The electric potential at the anode parts becomes different from the electric potential at the cathode parts. This electric potential difference causes corrosion current to flow between the anode parts and the cathode parts, which is a corrosion reaction. The corrosion current moves cations in city water to the cathode parts and anions therein to the anode parts. These movements of ions cause secondary reactions. The secondary reactions result in, for example, formation of calcium carbonate films on the surface of iron at the cathode parts, and formation of films containing red rust as a main component and silica substances on the surface thereof at the anode parts. The films formed at the cathode and anode parts check the movement of dissolved oxygen and various ions, which is necessary to the corrosion reaction. Thus the rate of corrosion on the inner walls of iron pipes is somewhat lowered. Although the corrosion rate is decreased, the corrosion reaction still continues and corrosion progresses because the films are not formed on the entire surface of the inner walls.
Researches by the inventors of the present invention revealed that the properties of the calcium carbonate films formed at the cathode parts by the corrosion reaction were changed by the treatment with a water quality-improving device, such as “THE BIOWATER”.
The inventors of the present invention also found the following: The calcium carbonate in the calcium carbonate films formed from water whose quality has not been improved with a water quality-improving device has a crystal structure of aragonite. The aragonitic crystals are in the form of needles, and the films thereof are rough and have small electric resistance. On the other hand, the calcium carbonate in the calcium carbonate films formed from water whose quality has been improved with a water quality-improving device has a crystal structure of calcite. The calcitic crystals are in the form of granules, and the films thereof are densely formed and have large electric resistance.
Calcium carbonate films become densely formed on the inner surfaces of pipes that contact water whose quality has been improved by the water quality improvement with the water quality-improving device, because the change in the crystal structure of calcium carbonate prevents dissolved oxygen from being supplied to the cathode parts. As a result of the formation of dense calcium carbonate films, the movement of dissolved oxygen that are necessary to corrosion reactions is prevented and the electric resistance of the calcium carbonate films becomes larger. Thus, the corrosion rate of iron on the inner surfaces of iron pipes is decreased.
The decrease in the corrosion rate also delays the growth of films of red rust, or iron oxide, at the anode parts, and further densifies red rust films per se.
As a result, the oxygen supply to the surface of the iron at the parts with red rust is decreased, which changes the red rust to black rust. In other words, the life of Wüstite (FeO) is made longer, which enables Wüstite to react with red rust (Fe2O3) to form magnetite. As time lapses, a dense black rust layer is formed from the surface side of the iron inner walls, which keeps iron atoms from being ionized.
The invention disclosed in patent document 1 teaches placing first electrodes in water whose quality is not improved, such as city water, and second electrodes in water whose quality is improved; measuring an electric resistance between the first electrodes and the second electrodes; and determining an improvement in water quality. The determination device for determining an improvement in water quality disclosed in patent document 1 is capable of determining an enhancement in the antirust effect of water in just a short period of several days, which is excellent performance.
However, determination devices for determining an improvement in water quality that require a shorter time period to determine an enhancement in the antirust effect of water whose quality has been improved are desired.
Conductivity meters, or electroconductivity meters, are commercially available. On the websites of business corporations that manufacture and sell commercially available conductivity meters are carried technological stories like the following: The degree of filthiness of industrial wastewater or of water discharged from sewage treatment plants is determined based on electric conductivity measured with a conductivity meter; pH and electric conductivity are effective as indicators to show the degree of rainwater pollution, and the degree is monitored with a conductivity meter; an electric conductivity of a food is measured with a conductivity meter and the salinity of the food is calculated from the resulting electric conductivity; and the electric conductivity measured with a conductivity meter is employed as an indicator of the purity of water when ultrapure water is produced. Judging from the stories on such websites, conductivity meters have been used mainly as a measuring instrument to measure electric conductivity.